The invention relates to an apparatus for heating water intended for the preparation of hot beverages. Such apparatus are known in the form of a reservoir in which a heating element is accommodated and to which a draw-off tap is connected. The known apparatus is filled with an amount of cold water, which amount is heated up to the desired temperature, whereupon a signal light indicates that the water has reached the desired temperature and warm water can be drawn off. When a given minimum water level is reached in the tank, drawing off can no longer take place and the tank should be replenished, whereupon one must wait until the water in the reservoir has again the desired temperature. Hence, the known apparatus provides a batchwise heating of a particular amount of water. The drawbacks thereof are that during the heating up of the amount of water introduced batchwise into the reservoir, no water of the desired end temperature can be drawn off, and the relatively long waiting period.
To overcome this drawback, there are also known apparatus comprising a reservoir in which a heating element and a draw-off tap are accommodated, the reservoir being connected to a water supply and the water level in the reservoir being kept substantially constant. In such an apparatus, as soon as water is being drawn off, the reservoir is replenished until the desired water level is reached. Drawbacks of this known apparatus are the long initial waiting period and the fact that when much water is drawn off successively, the temperature of the water in the reservoir drops as a consequence of the feed of cold water. Generally, the power of the heating element is insufficient for heating up the fed cold water quickly enough, so that the temperature of the water in the reservoir cannot be kept constant within a temperature range of .+-.3.degree.-4.degree. C.